Ontogeny of glycine-enhanced [3H]MK-801 binding to N-methyl-D-aspartate receptor-coupled ion channels

NMDA receptor involvement in spatial delayed alternation in developing rats

Two experiments examined the effect of the noncompetitive NMDA receptor antagonist, dizocilpine maleate (MK-801), on spatial working memory during development. Rats were trained on spatial delayed alternation (SDA) in a T-maze after ip administration of 0.06 mg/kg MK-801, 0.1 mg/kg MK-801, or saline on postnatal days (P) P23 and P33 (Experiment 1), or following bilateral intrahippocampal administration of 2.5 or 5.0 microg per side MK-801 or saline on P26 (Experiment 2). In Experiment 1, MK-801 dose-dependently impaired SDA learning at both ages. Because the same doses of systemic MK-801 have no effect on T-maze position discrimination learning, impairment of SDA by MK-801 likely reflects disruption of spatial working memory. Both doses of MK-801 abolished acquisition of SDA performance in Experiment 2. Disruption of hippocampal plasticity may account for the effects produced by systemic MK-801 administration. These results confirm and extend earlier lesion studies by implicating plasticity of hippocampal neurons in the ontogeny of spatial delayed alternation.

Behavioral analysis of the consequences of chronic blockade of NMDA-type glutamate receptors in the early postnatal period in rats

Considering data on the possible glutamatergic nature of the pathogenesis of schizophrenia, we attempted to model cognitive derangements in animals by chronic blockade of NMDA glutamate receptors. Wistar rats received daily s.c. injections of the non-competitive NMDA glutamate receptor antagonist MK-801 (0.05 mg/kg) from days 7 to day 49 of postnatal life. One day after the antagonist injections given on days 27 and 28 of life, animals of the experimental group showed decreased levels of spontaneous movement and orientational-investigative activity as compared with controls, where there was no change in the elevated locomotor reaction produced in response to the direct action of MK-801. These animals showed decreases in the level of anxiety (on day 40 of life) and derangement in spatial learning with food reinforcement (days 50-54 of life). It is suggested that early neonatal blockade of NMDA glutamate receptors leads to the development in animals of disturbances to situational perception and assessment of incoming sensory information.

Maturation of locomotor and Fos responses to the NMDA antagonists, PCP and MK-801

Antagonists at the N-methyl-D-aspartate (NMDA)-type glutamate receptor, such as phencyclidine (PCP) and dizocilpine (MK-801), are well-known to evoke increases in locomotor activity in adult rats and mice. However, little is known about the effects of NMDA antagonists on locomotor activity as a function of development. The present study examined locomotor responses to PCP or MK-801 in male rats of varying ages and found that prepubertal rats were more sensitive to the locomotor-elevating effects of PCP (1.5 mg/kg and 3. 0 mg/kg, s.c.) than were adults. Locomotor responses to MK-801 (0.1 and 0.2 mg/kg, s.c.) were not dependent on age. The age-dependent response to PCP may be related to developmental events in the motor cortex, since more Fos-immunoreactive neurons were observed in the motor cortex of prepubertal animals after PCP administration relative to adult animals. An opposite pattern of age-dependent Fos responses was observed in the posterior retrosplenial cortex. The results suggest that locomotor responses to NMDA antagonists can be influenced in an age- and drug-dependent manner and that maturational events in the motor cortex may modify responses to PCP.

Developmental maturation of the N-methyl-D-aspartic acid receptor channel complex in postnatal rat brain

The N-methyl-D-aspartate (NMDA) receptor plays an important role in developmental plasticity. Previous studies have reported differences between the NMDA receptor-channel complex in the rat pup brain and the adult brain. In the present study, modulation of the NMDA channel complex as a function of age was measured to determine when the temporal switching of the NMDA receptor from the immature form to the adult mature form takes place. [(3)H]MK-801 binding was measured in the rat forebrain from postnatal day 1 to day 21. Our data suggest the presence of two types of NMDA receptors - an immature type and a mature type. The immature NMDA receptor, seen during the early postnatal period (day 1-day 14) is highly sensitive to spermidine, L-glutamate alone potentiates [(3)H]MK-801 binding, and glycine failed to potentiate an L-glutamate-induced increase in [(3)H]MK-801 binding. During the late postnatal period (after day 14) spermidine alone did not increase [(3)H]MK-801 binding as potently as it did during the early postnatal period, high-affinity [(3)H]MK-801 binding was not seen in the presence of L-glutamate alone, and L-glutamate and glycine or L-glutamate and spermidine or L-glutamate, glycine and spermidine together, significantly increased [(3)H]MK-801 binding in a manner similar to that reported in the adult brain. Together, the pharmacology of the NMDA receptor during the early postnatal period differs from the adult-like receptor seen during the late postnatal period, and that in rats the apparent switching of the NMDA receptor from the immature type to the mature type takes place after the second postnatal week.

Differential changes in the subcellular distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate and N-methyl-D-aspartate receptors in neonate and adult rat cortex

We compared the distribution of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors and their individual subunits in synaptosomal and microsomal fractions prepared from 2-day-old (P2) and adult rat cortex. In P2 cortex more [3H]-(S)-fluorowillardiine ([3H]FW) binding to AMPA receptors was in the intracellular microsomal fraction than in the synaptosomal fraction whereas in adult rats the reverse was observed. Immunoblots with GluR1, GluR2/3, GluR4 and pan-AMPA antibodies showed the same profile. In contrast, the majority of [3H]MK-801 binding to the N-methyl-D-aspartate (NMDA) receptor and NR1 subunit immunoreactivity was present in the synaptosomal fraction at both developmental time points. These results suggest a developmental rearrangement of the distribution of AMPA receptors within neurons, a process which is likely to be important in synaptic stabilization and plasticity.

Biochemical studies of the structure and function of the N-methyl-D-aspartate subtype of glutamate receptors

The N-methyl-D-aspartate (NMDA) subtype of glutamate receptors plays a key role in synaptic transmission, synaptic plasticity, synaptogenesis, and excitotoxicity in the mammalian central nervous system. The NMDA receptor channel is formed from two gene products from two glutamate receptor subunit families, termed NR1 and NR2. Although the subunit composition of native NMDA receptors is incompletely understood, electrophysiological studies using recombinant receptors suggest that functional NMDA receptors consist of heteromers containing combinations of NR1, which is essential for channel activity, and NR2, which modulates the properties of the channels. The lack of agonists or antagonists selective for a given subunit of NMDA receptors has made it difficult to understand the subunit expression, subunit composition, and posttranslational modification mechanisms of native NMDA receptors. Therefore, most studies on NMDA receptors that examine regional expression and ontogeny have been focused at the level of the mRNAs encoding the different subunits using northern blotting, ribonuclease protection, and in situ hybridization techniques. However, the data from these studies do not provide clear information about the resultant subunit protein. To directly examine the protein product of the NMDA receptor subunit genes, the development of subunit-specific antibodies using peptides and fusion proteins has provided a good approach for localizing, quantifying, and characterizing the receptor subunits in tissues and transfected cell lines, and to study the subunit composition and the functional effects of posttranslational processing of the NMDA subunits, particularly the phosphorylation profiles of NMDA glutamate receptors.

Ontogeny of ethanol-induced locomotor activity and hypothermia differences in selectively bred FAST and SLOW mice

The replicate lines of selectively bred FAST and SLOW mice differ in locomotor response to 2 g/kg ethanol (EtOH). FAST mice show enhanced locomotion; SLOW mice exhibit no change or locomotor depression. Little is known about the responses of FAST and SLOW mice to EtOH during development. We assessed the locomotor responses of FAST and SLOW mice at postnatal days (P) 10, 15, 30, and 60. A genetically correlated response, EtOH-induced hypothermia, was also investigated. Although all animals demonstrated their respective selection phenotypes in adulthood, developing FAST mice exhibited ethanol stimulation by P15 (replicate 1) or P30 (replicate 2). At these ages, responses of FAST mice differed from those of SLOW. The stimulant response in FAST mice was adult-like at P30. EtOH-induced hypothermia was seen in SLOW mice by P15. These data suggest that sensitivity to the locomotor stimulant effects of EtOH changes during postnatal development, and may mirror developmental profiles for certain neurotransmitter systems.

Taurine, glutamate and GABA modulate the outgrowth from goldfish retinal explants and its concentrations are affected by the crush of the optic nerve

The amino acid taurine plays an important trophic role during development and regeneration of the central nervous system. Other amino acid systems, such as those for glutamate and gamma-aminobutyric acid (GABA), are modified during the same physiological and pathological processes. After crushing the optic nerve, goldfish retinal explants were plated in the absence and in the presence of different amino acids and amino acid receptor agonists. The length and the density of the neurites were measured at 5 days in culture. Taurine increased the length and the density of neurites. Glutamate and glycine increased them at low concentration, but were inhibitors at higher concentration. The combination of N-methyl-D-aspartate (NMDA) and glycine produced a greater inhibitory effect than NMDA alone. NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) added simultaneously with taurine impaired the stimulatory effect of the latter. GABA stimulated the emission of neurites in a concentration dependent manner. Hypotaurine also elevated the length of neurites, but cysteinsesulfinic acid did not produce a significant effect. The concentrations of taurine, glutamate and GABA were determined by HPLC with fluorescent detection in the retina of goldfish at various days post-crushing the optic nerve. The levels of taurine were significantly increased at 48h after the crush, and were elevated up to 20 days. Glutamate level decreased after the lesion of the optic nerve and was still low at 20 days. GABA concentration was not significantly different from the control. The interaction of these amino acids during the regenerative period, especially the balance between taurine and glutamate, may be a determinant in restoring vision after the crush.

Characterization of neuronal migration disorders in neocortical structures: quantitative receptor autoradiography of ionotropic glutamate, GABA(A) and GABA(B) receptors

Epileptiform activity was previously described [Luhmann et al. (1998) Eur. J. Neurosci., 10, 3085-3094] in the neocortex of the adult rat following freeze lesioning of the newborn neocortex. After a survival time of 3 months, a small area of dysplastic cortex surrounded by histologically normal (exofocal) neocortex was observed. The dysplastic cortex is characterized by the formation of a small sulcus and a three- to four-layered architecture. Two questions are addressed here: (i) is the hyperexcitability associated with changes in binding to major excitatory and inhibitory transmitter receptors in the dysplastic cortex?; and (ii) do such changes also occur in the exofocal cortex? Alterations in binding to glutamatergic N-methyl-D-aspartate (NMDA), (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), kainate and GABA(A) and GABA(B) (gamma-aminobutyric acid) receptors are demonstrated with quantitative in vitro receptor autoradiography by using the ligands [3H]MK-801, [3H]AMPA, [3H]kainate, [3H]muscimol and [3H]baclofen, respectively. In the dysplastic cortex, the binding to NMDA, AMPA and kainate receptors is significantly increased, whereas the binding to GABA(A) and GABA(B) receptors is reduced. Exofocal areas of the lesioned hemisphere show an imbalance between excitatory and inhibitory receptor binding with an up-regulation of the binding to AMPA and kainate, and a down-regulation to GABA(A) receptors. The binding to GABA(B) and NMDA receptors is not significantly changed in the exofocal areas. The imbalance between excitatory and inhibitory receptors may cause the hyperexcitability, as previously found in the identical experimental model, and may also induce epileptiform activity in the human cortex with migration disorders.

Acute and long-lasting effects of neonatal hypoxia on (+)-3-[125I]MK-801 binding to NMDA brain receptors

The NMDA receptor subtype is the major excitatory mediator for glutamate neurotoxicity. To assess its participation in the noxious effects of postnatal hypoxia, we have characterized the binding of the ionophoric marker of NMDA receptor, dizocilpine (MK-801). Binding of (+)-3-[125I]MK-801 to NMDA brain receptors under nonequilibrium conditions was quantified by in vitro autoradiography in rats exposed to hypoxia induced by 93% N2/6.5% O2 exposure for 70 min on Postnatal Day 4. Acute and long-lasting effects were investigated at 4 h after injury and on Postnatal Day 40. At the acute stage, a transient decrease in binding was found in several specific brain areas, hypothalamus, amygdaloid nuclei, entorhinal cortex, perirhinal cortex, and hippocampus, and no differences were found in temporal cortex, thalamus, and geniculate nucleus, when compared to sham-treated animals. At this early age, there was no increase of binding when slices from both groups were incubated in the presence of glutamate and glycine (Glu/Gly), positive allosteric modulators of MK-801 binding. In the 40-day-old brains, the binding to the NMDA receptors of hypoxiatreated animals was not different with respect to controls in most of the areas studied, but the Glu/Gly stimulation of binding in hypoxic rats showed a reduced, or absent, response to the allosteric modulators. In contrast, control rats showed a remarkable increase of the specific binding induced by the presence of the modulators in the incubation buffer. Binding of (+)-3-[125I]MK-801 was also performed at a higher concentration to clarify whether the altered response to Glu/Gly may be due to differences in the number of channels; however, the density of NMDA receptors at this concentration was similar in both control and hypoxia-treated rats. We conclude that the effect of exposure of newborn rats to hypoxia can generate acute and long-lasting effects on the NMDA receptor. The deleterious action of this kind of noxa on the CNS could be exerted by interference with normal glutamatergic transmission and hence over normal growth and development.

Effects of excitatory amino acids on the hypothalamic-pituitary-adrenal axis of the neonatal rat

Most stimuli that elicit a response by the hypothalamic-pituitary-adrenal (HPA) axis of adult rats fail to do so in infant rats aged 4-14 postnatal days (pnd). This interval is termed the stress hyporesponsive period (SHRP). The present study examined the development of the HPA response to the excitatory amino acids (EAAs), N-methyl-D-aspartic acid (NMDA) and kainic acid (KA), at 3 ages (i.e., pnd 6, 12, 18) during or immediately after the SHRP. Results indicate that intraperitoneal (i.p.) administration of 2.5 mg/kg KA or 5 mg/kg NMDA is capable of inducing age- and time-dependent elevations of ACTH and CORT, with KA being the more potent of the two EAAs. In contrast to other stimuli which are capable of eliciting an HPA response during the SHRP, NMDA and KA appear to possess more potent effects at earlier ages. Administration of lower doses of these EAAs did not elicit an HPA response. Pretreatment with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 0.69 mg/kg i.p.), a KA receptor-specific antagonist, attenuated the effects of KA. These results suggest that KA exerts its effects via the KA receptor and that this receptor appears to be mature at both pnd 12 and 18. In contrast, pretreatment with D,L-2-amino-5 phosphonovaleric acid (APV; 7.5 mg/kg i.p.), an NMDA receptor-specific antagonist, was only effective at pnd 18 suggesting that the NMDA receptor is not yet mature at pnd 12. Finally, EAAs induce age- and time-dependent behavioral modifications (i.e., hindpaw scratching and hyperlocomotion). These effects, however, appear to only contribute to, but not cause, the endocrine responses.

Ontogeny of NMDA R1 subunit protein expression in five regions of rat brain

A polyclonal antiserum to a fusion protein corresponding to a region of the NMDA R1 (NR1) subunit (amino acids 656-811) was produced and affinity purified. A quantitative immunoblotting technique was developed using the fusion protein as a standard. By employing this method, ontogenic studies (day 2-42) of the density of NR1 protein were carried out in several regions of rat brain. The results showed that in all five of the brain regions examined [olfactory bulb (Ob), cortex (Cx), hippocampus (Hp), midbrain (Mb) and cerebellum (Cb)], levels of NR1 protein are low at birth and increase with similar patterns having a sharp rise within the first 3 weeks after birth. Levels increased 2.0 to 4.5-fold from postnatal day 2 to postnatal day 42. Although the general patterns of developmental expression are similar, large differences in the absolute amounts of NR1 protein among the five brain regions were observed. The maximal levels (pmol of fusion protein equivalent/mg +/- S.E.) of NR1 subunit attained during development in the five regions are: Hp 2.0 +/- 0.37 > Cx 1.4 +/- 0.11 > Ob 1.3 +/- 0.2 > Mb 1.0 +/- 0.10 > Cb 0.57 +/- 0.13. The temporal patterns of expression of NR1 protein are similar to results from studies examining the expression of NR1 mRNA. Furthermore, the absolute numbers obtained from our studies are close to those found using [(3)H]MK-801 binding suggesting that many of the NR1 subunits expressed in the brain exist in an active form.

Dizocilpine binding to cerebral cortical membranes from developing and ageing mice

The binding of [3H]dizocilpine (MK-801) to the N-methyl-D-aspartate (NMDA)-gated ion channel was characterized in cerebral cortical membranes during the major portion of the mouse life-span (from 7-day- to 22-month-olds). The binding was saturable, consisting of only one component at all ages studied. The maximal binding capacity Bmax was very substantial in 14-day-old mice when compared to adults (3-month-olds), decreasing thereafter during ageing. The binding constant KD remained unchanged during development and increased only slightly in aged mice. Glutamate and glycine potentiated dizocilpine binding concentration-dependently. Their efficacy varied markedly with age. Both glutamate and glycine had considerably less effect on the immature cerebral cortex and in the oldest group of mice (22-month-old) than in young adults. The marked increase in dizocilpine binding sites at the age of 2 weeks coincides with the previously reported transient increase in NMDA binding sites in the cerebral cortex. The weak potentiation of dizocilpine binding by glutamate and glycine in the immature brain could be a factor which protects neurons during this period from excitotoxicity and increased susceptibility to seizures induced by acidic amino acids. The decrease in the number of dizocilpine binding sites during ageing could result partly from the loss of cortical neurons.

Developmental alterations in NMDA receptor-mediated [Ca2+]i elevation in substantia gelatinosa neurons of neonatal rat spinal cord

Using spinal cord slices prepared from neonatal rats, the intracellular free Ca2+ concentration ([Ca2+]i) in neurons located in the dorsal horn substantia gelatinosa (SG) was measured with microscopic fluorometry by loading fura 2-AM into neurons. Developmental alterations in the elevation of [Ca2+]i elicited by the glutamate analogs, NMDA and AMPA, were investigated from postnatal day (PNDs) 1 to 17. During the 1st week of postnatal life, when neuronal maturation of the SG is known to take place, the NMDA response remained large or even slightly increased. It subsequently showed a gradual decline. This pattern of postnatal changes is consistent with previously reported autoradiographic studies on NMDA-binding sites. The affinity of receptors for NMDA was found to decrease constantly during the period examined. The AMPA response and resting [Ca2+]i showed no significant developmental changes. Neonatal treatment with capsaicin, which has been shown to degenerate fine primary afferent fibers terminating in the SG, delayed the developmental decline in the NMDA-induced [Ca2+]i response. It is suggested that the number and the molecular properties of NMDA receptors expressed in the SG change during early postnatal neuronal maturation. The temporal coincidence between postnatal alteration in NMDA-induced [Ca2+]i elevation and neuronal maturation of the SG may indicate that intracellular Ca2+ regulated by NMDA receptor activation is related to postnatal neuronal maturation. Activation of fine primary afferent fibers may contribute to the observed developmental alterations in the NMDA response of SG neurons.

Regional profile of developmental changes in the sensitivity of the N-methyl-D-aspartate receptor to polyamines

The NMDA receptor exhibits increased sensitivity to stimulation during early development compared with the adult. In this study, we examined modulation of the NMDA receptor by polyamines during development to see if it correlates with differences in the functional responsiveness of the NMDA receptor. [3H]MK-801 binding was measured in discrete brain regions in the presence and absence of polyamines in 3-, 7-, 15-, 25-, and 60-day-old Sprague-Dawley rats. [3H]MK-801 binding increased between postnatal days 3 and 15, with adult levels of binding being reached between days 15 and 25. Spermidine (75 microM) caused maximal stimulation of [3H]MK-801 binding during early development, ranging from 250% in the thalamus to 450% in the caudate putamen at postnatal day 3. This effect gradually declined to levels seen in the adult by postnatal days 15-25. During all developmental stages, the stimulation seen was greater in the caudate putamen compared with the hippocampus. Diethylenetriamine (1 mM) exhibited similar developmental and regional heterogeneity in its effects on [3H]MK-801 binding, producing substantial stimulation of binding in the neonate, but not in the adult. The EC50 and Emax values for the stimulatory effect of spermidine were significantly higher at day 7 compared with the adult. Unlike spermidine and diethylenetriamine, there was no regional variation in the effects of the putative "polyamine site" inverse agonist 1,10-diaminodecane at any age and only a slightly attenuated inhibition at postnatal day 3 compared with the adult.(ABSTRACT TRUNCATED AT 250 WORDS)

A glycinergic intervention potentiates the antiseizure efficacies of MK-801, flurazepam, and carbamazepine

Twenty four hours after mice were forced to swim for up to 10 minutes in cold water, there was a reduction in the ability of MK-801 to antagonize the electrical precipitation of tonic hindlimb extension. Milacemide, a lipophilic prodrug of glycine, restored the antiseizure efficacy of MK-801 to the same level observed in unstressed animals treated with milacemide and MK-801. Stimulation of the glycine-gated chloride ionophore subsequent to the liberation of free glycine could explain milacemide's pharmacologic action as an adjuvant to MK-801. Consistent with this interpretation, milacemide was able to potentiate the antiseizure effects of flurazepam, a benzodiazepine agonist, in stressed and unstressed mice and carbamazepine in unstressed animals. D-cycloserine, a partial glycine agonist with greater specificity for the strychnine-insensitive modulatory site on the NMDA receptor complex, was examined for its effect on MK-801's antiseizure efficacy. At a high dose (320 mg/kg), D-cycloserine alone had an anticonvulsant effect. Moreover, this dose of D-cycloserine administered with MK-801 showed a significantly greater anticonvulsant efficacy than MK-801 alone. The data support the development of glycinergic interventions as adjunctive agents in the pharmacotherapy of seizure disorders.

Expression of the gene coding for the NR1 subunit of the NMDA receptor during rat brain development

Expression of the gene coding for the NR1 subunit of the N-methyl-D-aspartate (NMDA)-type of glutamate receptor was investigated in the developing rat brain. Peak NR1 gene expression in the whole brain occurred at approximately postnatal day (P) 10 with a second increase in the adult. To determine the ontogenic expression in the various brain regions, the expression of NR1 at P2, P10 and P60 was compared. The regional studies indicated increased expression at P60 in the cerebellum. In the midbrain and diencephalon, levels of expression at P10 and P60 were higher than at P2, while in the hippocampus, expression at P10 was significantly higher than at either P2 or P60. Expression in the other brain regions was constant over the period studied. These data indicate a region-specific expression of NR1 in the central nervous system during ontogeny.

Strychnine-insensitive glycine binding to cerebral cortical membranes in developing and ageing mice

The strychnine-insensitive binding of [3H]glycine was characterized in purified cerebral cortical membranes from mice aged from 7 days to 22 months. The binding was saturable, exhibiting only one component during the whole life-span studied. The binding constant KD did not change during development and ageing, whereas the maximal binding capacity Bmax, calculated per protein content, increased up to the age of two weeks and then again in ageing animals (18- and 22-month-olds). The binding was similarly inhibited by the antagonists 7-chlorokynurenate, 3-amino-1-hydroxypyrrolidin-2-one (HA-966) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in 7-day-, 3-month- and 12-month-old mice. The inhibition caused by glycine, L-serine and beta-alanine also remained unaltered during the whole life-span. beta-Alanine was a noncompetitive inhibitor. The alterations in the maximal binding capacities during development and ageing could be of importance in the regulation of NMDA receptors, which have been implicated in synaptic potentiation, developmental processes and various pathological conditions.

Quantitation of NMDA receptor (NMDAR1) mRNA levels in the adult and developing rat CNS

A rapid and sensitive solution hybridization assay was used to quantitate N-methyl-D-aspartate (NMDA) receptor mRNA levels in the central nervous system (CNS) of rat, mouse and human. A riboprobe labelled with 32P was prepared from a plasmid containing a 1413 base sequence from the cDNA for the functional rat NMDA receptor subunit, NMDAR1. Using a full length sense transcript as the calibration standard, the assay reliably measures 8 pg of NMDAR1 mRNA. When expressed as pg of NMDAR1 mRNA/micrograms total cellular RNA, the highest levels in the adult rat CNS are in the olfactory bulb (20.9 pg/micrograms RNA) and the lowest levels are in the spinal cord (5.2 pg/micrograms RNA). Intermediate levels were found in frontal cortex, hippocampus, cerebellum and whole brain. In the mouse CNS the highest levels of NMDAR1 mRNA were found in the olfactory bulb (12.9 pg equivalents/micrograms RNA), followed closely by hippocampus, frontal cortex and cerebellum. Mouse spinal cord (4.4 pg equivalents/micrograms RNA) had the lowest levels of NMDAR1 mRNA. The NMDAR1 riboprobe hybridizes with the same size transcripts in Poly(A)+ RNA from rat, mouse and human brain. In the developing rat, NMDAR1 mRNA levels in frontal cortex and hippocampus increased nearly 3 fold from postnatal day 3 to day 15 and approximately doubled from day 15 to day 67 (adult). Therefore, from postnatal day 3 to adult (day 67) frontal cortex and hippocampus levels of NMDAR1 mRNA increased nearly 6 fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Excitatory amino acid regulation of the enkephalin phenotype in mouse embryonic spinal cord cultures

Expression of the preproenkephalin gene in developing spinal cord-dorsal root ganglia (SC-DRG) cultures was determined by Northern analysis following treatments with different agonists and antagonists of the glutamate receptor. Cultures (10-12 days old) were treated with various concentrations (10(-7)-10(-3) M) of N-methyl-D-aspartate (NMDA), quisqualate, kainic acid (KA), 2-amino-5-phosphonovaleric acid (APV) and 5-methyl-10,11-dihydro-5H-dibenzo[a, d]cyclohepten-5,10-imine maleate (MK801) either with or without blocking spontaneous electrical activity with 1 microM tetrodotoxin (TTX). In electrically active cultures, treatments with NMDA and KA increased preproenkephalin transcripts (mRNAppENK), showing maximum effects at 1 microM (4-fold and 2-fold, respectively), while treatments with quisqualate and MK801 caused concentration-dependent down-regulation in mRNAppENK. The most effective concentrations of NMDA (1 microM) and quisqualate (10 microM) altered mRNAppENK levels within 4 h of treatment and peaked after 24 h for NMDA and 48 h for quisqualate treatment. Co-treatment with APV completely blocked the NMDA-induced rise of mRNAppENK. During electrical blockade, none of the concentrations of NMDA tested showed any effect on enkephalin expression, neither could NMDA pre-treatment prevent the TTX-induced down-regulation of mRNAppENK. Our results indicate that the activity-dependent establishment of the enkephalin phenotype is modulated through the selective activation of the NMDA-glutamate receptor.

Development of dopamine and N-methyl-D-aspartate systems in rat brain: the effect of prenatal phencyclidine exposure

Phencyclidine (PCP) inhibits the uptake of the neurotransmitter dopamine (DA), and blocks N-methyl-D-aspartate (NMDA) receptor-regulated ion channels. PCP also binds to sigma receptors in vivo and in vitro in rat brain. Prolonged exposure to PCP in adults has been observed to reduce the number of PCP binding sites in brain. We designed these experiments to evaluate whether prolonged prenatal exposure to PCP produces alterations in the development of DA and NMDA systems in brain. To do so, we characterized the normal course of development of basal and stimulated DA release in striatal slices, the ontogeny of striatal DA concentrations, and the development of NMDA receptor channels and associated glutamate binding sites in frontal cortex. We compared these developmental profiles to those in rats exposed to prenatal PCP, in an attempt to characterize the effect of prenatal PCP exposure on the pattern of brain development. Pregnant CD rats were injected s.c. with either 0, 10 or 20 mg/kg PCP daily on gestational days 8 through 20. On postnatal days (PND) 8, 21, 45, or 100, rats were sacrificed and brain tissues isolated for in vitro assessment. In vitro [3H]DA release from striatal slices evoked by either 40 microM glutamate or 15 mM K+ increased over 250% from PND 8 to PND 45, and glutamate-stimulated release was still significantly below adult levels at PND 45. In contrast, D-methamphetamine (D-METH)-evoked [3H]DA release, frontal cortical glutamate binding sites and NMDA channels developed early, reaching adult levels on or before PND 21.(ABSTRACT TRUNCATED AT 250 WORDS)

The ontogeny of phencyclidine-induced wall climbing and locomotor activity

Wall climbing behavior is an age-specific behavior that is elicited during postnatal Days 7 through 17 by various stimuli that include heat, odors, shock, and the catecholaminergic agonists apomorphine, amphetamine, and clonidine. In a previous study, a significant amount of wall climbing behavior was observed during ataxia and activity testing following phencyclidine (PCP) administration in Day 19 but not Day 40 rat pups. The present study describes the ontogeny of PCP-induced wall climbing behavior and locomotor activity. Frequency and duration of wall climbing bouts and locomotor activity were recorded on Days 5, 12, 19, 26, 33, or 40 following PCP treatment. On Day 12, all doses of PCP induced significant amounts of wall climbing behavior. A similar pattern of results was observed on Day 5 although these effects were not statistically significant. After Day 12, PCP-induced wall climbing behavior declined precipitously. PCP increased locomotor activity at all ages tested with maximum activities observed on Day 19. These results demonstrate that PCP-elicited wall climbing behavior follows an ontogenetic profile similar to that previously reported for other stimuli and that there are robust ontogenetic differences in the locomotor response to PCP.